Battery technology has not kept pace with recent growth in the number, variety, and capability of embedded and portable digital electronics. Energy harvesting from human or environmental sources is a promising alternative, and active harvesting has already seen commercial applications in wind-up and shake-to-recharge electronics. However, passive energy harvesting using mechanical vibration as a power source has potentially wider application in wearable and embedded sensors, as either a complement or replacement for batteries or solar energy harvesting. Two applications--one computing an FFT to monitor a shipboard gas turbine's vibrations and the other using data from a wearable acoustic biomedical sensor to analyze a user's exertion state--illustrate the range of requirements. The SensorDSP is a chip implementation for a wearable biomedical sensor.